Issue
An error of "The request sent to this API connection does not have a correct salesforce.com URL. Please have your salesforce.com administrator contact support." is received after updating to Salesforce Spring '18.
Resolution
- Navigate to Setup-->Critical Updates
- Please ensure the following Critical updates are deactivated:
- "Remove Instance Names From URLs for Visualforce, Community Builder, Site.com Studio, and Content Files"
- Clear the Browser Cache
- Log out of Salesforce
